Imaging systems available today include one in which, for example, a television (TV) signal generated by a TV camera or a video signal recorded on a video floppy disc by an electronic still camera is inputted to a computer system to be displayed on a monitor in a particular form such as, for example, a Video Graphics Array (VGA) form. This prior art imaging system as shown in FIG. 7 includes a personal computer 10 and an image recording and reproducing device 12 which are interfaced to each other by an electronics board 97. When the recording and reproducing device 12 is loaded with a video floppy disc 18 to read a video signal representative of a real image, the video signal is transformed into corresponding digital data by an analog-to-digital converter 98 of electronics board 97 and then developed as bit-mapped data in a dedicated video frame memory 99 also included in the electronics board. The personal computer 10 may then fetch the bit-mapped data later as needed and, thereafter, handle the data as a VGA image including displaying the data on VGA monitor 16.
Also, graphics in a VGA format generated by a personal computer may be converted to video signals capable of being recorded on a video floppy disc by an electronic still camera using conventional techniques as shown in FIG. 6. In FIG. 6 PC graphics are stored in a dedicated Buffer 1 and are read out by scan converter 2 along line 3 using a read-out rate dependent on the particular type of video signal format desired. In the figure an NTSC video signal capable of being recorded on a video floppy disc is shown as an output of scan converter 2. However, different scan rates, for example, PAL or SECAM scan rates, may also be used. The resultant NTSC signal in the figure may then be displayed on NTSC monitor 24.
As shown in FIGS. 6 and 7, it is known to provide a conversion from VGA to NTSC and vice versa. However, using the circuits of FIGS. 6 and 7, separate and independent hardware is required to store the video signal in its present state before it is converted. For example, in FIG. 6 a dedicated PC Graphics Buffer 1 must be provided to store the VGA signal before it is converted to NTSC by scan converter 2 since the VGA data must be arranged in a predetermined way so that the fixed rate scan converter 2 may properly access it in order to transform the signal to NTSC. Likewise, in FIG. 7 a dedicated frame memory 99 must be provided to store an NTSC signal before it is converted to VGA by the fixed-rate read-out operation of personal computer 10. Therefore, a large amount of hardware is needed in order to convert NTSC video signals to VGA and vice versa.
It is also known to insert (overlay) a computer graphics (VGA) signal in selected locations of an NTSC image and to display the thus-combined video signal onto an NTSC monitor such as a conventional TV receiver. Such a conventional system is shown in FIG. 8. An interlaced NTSC video signal is input to input terminal 202 and supplied to video combiner 203. A synchronization component of the input NTSC video signal is supplied to Gen-lock circuitry 201 which provides an output to video format converter 200. Non-interlaced VGA signals are pre-stored in PC graphics memory 100 and are supplied to scan-rate converter 200 which modifies the scan rate of the input non-interlaced VGA signals based on the output of the Gen-lock circuitry 201. The Gen-lock circuitry 201 receives the synchronization component of an input video signal, in this case NTSC, and provides an output to video format converter 200 so that the converter 200 can modify the format of its input, in this case VGA from PC graphics memory 100, so that the output of the converter 200 has a format equal to the input signal to the Gen-lock circuitry 201.
In FIG. 8 the converter 200 modifies the non-interlaced VGA input into interlaced VGA in the NTSC format and supplies the interlaced VGA to video combiner 203. At this point the VGA signal is of the same format (i.e., interlaced) as the NTSC video signal which is also supplied to video combiner 203. The output 204 of combiner 203 is an interlaced VGA signal overlaid onto an NTSC signal.
It is also known to overlay NTSC video signals onto VGA signals and to display the result onto a VGA monitor using prior art systems. However, a dedicated VGA Buffer and a dedicated NTSC video memory are required in the prior art systems.
As is clear from the description of the prior art systems above, a separate and dedicated frame memory or Buffer is required to hold each type of image signal, since a different type of image signal has a different format (i.e., interlaced or non-interlaced). For example, in FIG. 7 a separate dedicated frame memory 99 is required to store the NTSC signal before it is converted to VGA. Further, a separate and dedicated PC Graphics buffer (1,100) is required in FIGS. 6 and 8, respectively, in order to store VGA signals.
Since dedicated buffers or memories have been required by the prior art, a large amount of hardware is necessary in order to provide image signal processing equipment capable of handling a variety of image signal formats.
A video signal processing apparatus has been described in co-pending application Ser. No. 08/003,829 and involves a system for converting one of NTSC type and VGA type video signals to the other or overlays the two types of video signals and outputs them as either an NTSC type overlaid video signal or a VGA type overlaid video signal. The processing system has two video memories for storing video data. One of the two video memories stores solely VGA type video data. The other video memory stores either VGA type video data or NTSC type video data depending upon the particular function being carried out by the processing system. Video data may be read out from the other video memory using different scan rates so that an individually dedicated memory is not required for each type of video data in performing the above-mentioned conversions and overlays.
In the above-mentioned system, video output signals representing a mixture of a computer graphics (VGA) image and an NTSC-type image are easily displayed on a selected one of a computer graphics (VGA) type monitor or an NTSC-type monitor. However, the combined (overlaid) video image signals are not so easily sent on to an external memory. Difficulties arise in attempting to store an overlaid video signal in an external memory because the speed of the overlaid signal as it comes out of the above-mentioned video processing system is too fast for an external memory to handle. For example, the overlaid signals are sent out at a rate in the Megahertz (Mz) region. It would be useful to be able to store overlaid images in an external memory as an alternative to merely displaying the overlaid image onto a monitor display. By storing overlaid images in an external memory they would be able to be easily and selectably read out and displaced on a monitor at a later time without having to re-overlay the image signals making up the composite overlaid signal. Also, further processing or overlaying of the overlaid signals would be simplified.